The present invention relates to fiber optic sensors, and more specifically to a fiber optic sensor and method in which plural ambient conditions are determined.
Fiber optic systems for sensing ambient conditions at otherwise inaccessible locations are known. For example, fiber optic sensors may be used to monitor blood pressure inside a blood vessel. In such systems, as shown by way of example in FIG. 1, a fiber optic cable 12 is provided with a sensor 14 at a remote end that is placed where the blood pressure is to be measured. A source of light 16, such as a light emitting diode (LED), transmits a light signal through the cable 12 to the sensor 14 at the remote end. The sensor 14 may include two semi-reflective surfaces 18 and 20 that are spaced from each other by a distance D1 that varies as a function of the pressure on the sensor 14. The surface 18 partially reflects and partially transmits the received light signal, while the surface 20 reflects the light transmitted through the surface 18. The partially reflected light from the surface 18 and reflected light from surface 20 cause an interference pattern to form in the cable 12. The intensity of the light in the cable will vary as the distance between the two surfaces changes in response to blood pressure changes. The intensity may be sensed to thereby indicate changes in blood pressure. See, for example, U.S. Pat. No. 4,709,413 issued Nov. 24, 1987 to Forrest, et al.
There are several problems with such systems that limit their usefulness. First, they are only able to measure one condition. If the changes in a second condition, such as temperature, are also desired, a second cable with a separate sensor must be provided. A second cable increases complexity and cost, and more importantly it may not be possible to insert a second cable in a narrow channel. Further, sensors for measuring one condition such as pressure are typically also sensitive to another condition such as temperature so that they do not give an accurate reading of pressure if temperature changes.
Accordingly, it is an object of the present invention to provide a novel optical sensing method and device that obviates the problems of the prior art.
It is another object of the present invention to provide a novel optical sensing method and device in which plural ambient conditions are measured with a single optical fiber.
It is yet another object of the present invention to provide a novel optical sensing method and device in which plural serially aligned sensors at the end of a single optical fiber sense different ambient conditions.
It is still another object of the present invention to provide a novel optical sensing method and device in which plural serially aligned sensors at the end of a single optical fiber partially reflect and partially transmit an optical signal to form an interference pattern in the optical fiber.
It is a further object of the present invention to provide a novel optical sensing method and device in which plural serially aligned sensors at the end of a single optical fiber form an interference pattern in the fiber that is a function of each of the ambient conditions separately sensed by the plural sensors.
It is yet a further object of the present invention to provide a novel method and device for remotely sensing plural ambient conditions in which plural serially aligned sensors in an optical fiber include semi-reflective ends for reflecting an optical signal to form an interference pattern in the optical fiber that is a function of the distances between the semi-reflective ends of each sensor.
It is still a further object of the present invention to provide a novel method and device for remotely sensing plural ambient conditions in which plural serially aligned sensors in an optical fiber include semi-reflective ends for reflecting an optical signal to form an interference pattern and in which the reflectivities of each sensors' ends are chosen to simplify the evaluation of the ambient conditions.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of the preferred embodiments.